Project Summary/Abstract A hallmark of aging is difficulty understanding speech spoken rapidly or in noisy or reverberant conditions. This problem is common even among older adults who do not have hearing loss. However, it is aggravated by hearing impairment, and among those so impaired, is not corrected through hearing aid use. In a 2001 survey of 25 million Veterans, 46% (11.5 million) were over age 55. Of those over 55, 55% (6.3 million) reported a hearing condition that required a hearing aid. The VA spent $288 million on rehabilitation for hearing loss in 2006. Even though many Veterans are older and have hearing loss, and the VA spends millions of dollars on the problem of hearing impairment, progress is slow to lessen the impact of aging on hearing. One reason for this may be that aging is known to impair temporal processing, an ability thought to influence the understanding of rapid, noisy, or reverberant speech. Yet current therapeutic strategies including hearing aids do not address temporal processing impairments. The goal of this research is to better understand the psychophysical and physiological processes that limit speech understanding in the elderly. Objectives are to: Determine the extent to which (1) aging slows word recognition speed in noise; (2) those measures of temporal processing impacted by aging are associated with word recognition speed; (3) neural processing of brief stimuli can predict behavioral sensitivity to the temporal properties of those same brief stimuli. Ultimately, we plan to use mechanistic and site of lesion evidence arising from this research to develop audiometric tests and therapies to address the auditory rehabilitation needs of individual Veteran patients. Experiments are designed to examine relationships between perceptual and physiological measures of temporal processing and the processing time needed by older adults to accurately, confidently recognize speech. Subjects' performance will be evaluated for a time-gated word recognition task, in which recognition is measured in noise as a function of the portion of the word presented. Performance on this task is thought to be related to the real time perceptual encoding of words. Discrimination of silent intervals and envelope modulation will be used to obtain information about temporal fine structure and envelope processing because it is not yet clear which of these abilities would be most important for rapid recognition of words. Compound action potentials (CAPs) and auditory brainstem responses (ABRs) recorded in forward and simultaneous masking paradigms will be used to determine the levels of early neural processing that contribute to temporal processing abilities. Mixed-effects general linear modeling will be used to relate psychophysical and physiological temporal processing to word recognition speed. An otoacoustic emission (OAE) based estimate of cochlear function and a reading based estimate of cognitive processing speed will be covariates in the model. Participants will be younger and older adults with a range of hearing thresholds. We hypothesize that temporal fine structure processing and temporal responsiveness measured at the level of the brainstem will be strong predictors of the speed with which older adults recognize words. Associations with auditory nerve function are also expected, as opposed to higher level cognitive impairments of temporal processing. Results of the proposed work will lead to approaches to clinically distinguish among functional and structural stages at which temporal processing can be impaired, which would require substantially different remediation strategies. Results will also allow us to test current theories of temporal processing. Veterans that have suffered traumatic brain injury (TBI) could also potentially benefit from this work because, similar to age-based declines in auditory function, TBI may cause auditory impairment greater than hearing would suggest because of impaired temporal processing.